Rotary machine

ABSTRACT

To reduce the size of a rotary machine and to provide a rotary machine in which it is possible to achieve an improvement in reliability and performance of the rotary machine. A first casing ( 1 ) and a second casing ( 2 ) formed by dividing a substantially cylindrical casing ( 101 ), enclosing in the interior thereof a rotor shaft ( 4 ) in which rotor blades ( 11 ) are embedded, into two at substantially a central portion relative to an axial direction of the rotor shaft ( 4 ) are provided; a first coupling flange ( 1 A) and a second coupling flange ( 2 A) are provided at openings in the first casing ( 1 ) and the second casing ( 2 ), respectively; a third coupling flange ( 3 A) is provided, which is enclosed by the casing ( 101 ), which is positioned at substantially a central portion of the length in the axial direction in a substantially cylindrical blade ring ( 3 ) holding stator blades ( 10 ) and enclosing the rotor shaft ( 4 ), and which holds the blade ring ( 3 ); the first casing ( 1 ), the second casing ( 2 ), and the blade ring ( 3 ) being assembled by sandwiching the third coupling flange ( 3 A) between the first coupling flange ( 1 A) and the second coupling flange ( 2 A).

TECHNICAL FIELD

The present invention relates to a rotary machine used for a steamturbine, a gas turbine, or the like.

BACKGROUND ART

Generally, a casing used for a steam turbine or a gas turbine is dividedinto two, i.e., an upper casing and a lower casing in which a rotorshaft is incorporated, and these casings are coupled to each other on ahorizontal surface using a bolt (see Patent Japanese Unexamined UtilityModel Application, Publication No. S60-195908, for example).

Alternatively, in a turbine so-called “pot-like turbine”, the casing isintegrally formed as one piece, a rotor shaft portion is inserted fromone end opening of the casing, and the end opening is hermeticallyclosed by fastening a screw ring which is engaged with a screw portionprovided on an inner periphery of the casing (see Patent JapaneseUnexamined Patent Application, Publication No. S59-213907, for example).

It is an object of the casing structure described above is to securerigidity of the entire apparatus with respect to working fluid havinghigh temperature and high pressure, and to prevent leak of the workingfluid.

In the casing structure in which the casing is divided into two on thehorizontal surface as described above, the upper casing and the lowercasing are provided on entire peripheries of the horizontal surfacesthereof with joining flanges, which project from the entire periphery ofthe horizontal surface of the casing and thus there is a problem thatthe joined casing itself is increased in size.

Further, when the casing is increased in size, there is a problem thatthe mass of the entire turbine is increased, and costs for the materialcost and production are increased.

If the working fluid leaks from the joining surface between the uppercasing and the lower casing, there is a concern that performance of theturbine is affected. However, when the casing is divided into two on thehorizontal surface, the joining surface extends over the entireperiphery of the horizontal surface of the casing, and thus there is aproblem that a range is increased from which the working fluid leaks. Inthe above-described structure, since a penetrating portion of the rotorshaft is located on the joining surface of the casing, there is aproblem that the working fluid leaks easier.

In the pot-like casing structure, it can be considered that the rangefrom which the working fluid leaks can be reduced as compared with acase where the casing is provided on the entire periphery with thejoining flanges. However, the above structure in which the casing ishermetically closed can be employed only to a relatively small turbine,and such a structure must be replaced with a structure provided withflanges in a large turbine. In this case, there are problems that theflange and the joining bolt project in the axial direction, the entirelength of the casing is increased, and the entire rotary machine isincreased in size.

For example, in a turbine using a working fluid including a certainmaterial that must be carefully handled, it is not allowed to leak theworking fluid to atmosphere. Thus, a pressure vessel (outer casing)which further covers the casing is provided, a clean fluid which is notcontaminated by the certain material is charged under higher pressurethan the working fluid in a space between the pressure vessel and thecasing, thereby preventing the fluid in the casing from leaking outside(see FIG. 5).

FIG. 5 shows a configuration in which a casing 101 of the turbine bodydescribed above is accommodated in a pressure vessel (outer casing) 200.Constituent parts of the turbine are accommodated in the casing 101 (notshown). A rotor shaft 4 penetrates the casing 101 and the pressurevessel 200. A clean fluid which has pressure higher than the workingfluid in the turbine and which is not contaminated by a certain materialis charged in a space 201 between the casing 101 and the pressure vessel200 so as to prevent the fluid in the casing 101 from leaking outside.However, in the above-described configuration, because of increase insize of the casing 101, the pressure vessel 200 is also increased insize.

When the interior of the above turbine is contaminated with a certainmaterial, the turbine cannot be opened and inspected on a site in itsinstalled state for safety reasons unlike a general gas turbine or asteam turbine. Therefore, it is necessary to open and inspect theturbine after moving each turbine casing from the turbine room to aspecial maintenance area. In such a case, there are problems that,because of increase in size of the casing, it is difficult to securerigidity of the room, and a crane capacity for hoisting the casing islargely affected.

In the pot-like casing structure described above, a blade ring whichholds turbine stator blades is mainly supported at the end opening.However, in this state, the blade ring is supported in a cantilevermanner. Especially in a large turbine, when the blade ring is supportedin a cantilever manner, an overhang of the blade ring is made longer andthus, there are problems that a center is not sufficiently be held, andinfluence of a difference in thermal extension in the axial directionbetween a rotating portion and a stationary portion is increased.

DISCLOSURE OF INVENTION

The present invention has been accomplished to solve the above problems,and it is an object of the present invention to provide a rotary machinewhich can be reduced in size and which can enhance reliability andperformance.

In order to achieve the above object, the present invention provides thefollowing means.

In a casing structure of a turbine according to an aspect of the presentinvention, a first casing and a second casing formed by dividing asubstantially cylindrical casing, enclosing in the interior thereof arotor shaft in which rotor blades are embedded, into two atsubstantially a central portion relative to an axial direction of therotor shaft are provided; a first coupling flange and a second couplingflange are provided at openings in the first casing and the secondcasing, respectively; a third coupling flange is provided, which isenclosed by the casing, which is positioned at substantially a centralportion of the length in the axial direction in a substantiallycylindrical blade ring holding stator blades and enclosing the rotorshaft, and which holds the blade ring; the first casing, the secondcasing, and the blade ring being assembled by sandwiching the thirdcoupling flange between the first coupling flange and the secondcoupling flange.

According to the above aspect, the casing is divided into two in theaxial direction, for example on a division surface intersecting with therotor shaft, and the casing can be reduced in size as compared with acase where the casing is divided into two on the horizontal surface,e.g., on a division surface extending along the rotor shaft.

More specifically, when the casing is divided into two on the horizontalsurface, coupling flanges used for fastening the divided casings to eachother project outward from the entire periphery of the casing. In ageneral steam turbine or a gas turbine, a cross sectional area of acasing divided into two on vertical surface perpendicular to the rotorshaft becomes smaller than a horizontal cross section of a casingdivided into two on the horizontal surface. Therefore, in the casingwhich is divided into two (first casing and second casing) in the axialdirection, the projecting range of the coupling flanges can be madesmaller as compared with the casing divided into two on the horizontalsurface. In this configuration, the casing can be reduced in size.

According to the above aspect, the third coupling flange which extendsfrom the blade ring in a direction intersecting with the axialdirection, more preferably, in a substantially vertical direction, issandwiched between the first coupling flange of the first casing and thesecond coupling flange of the second casing which are divided in theaxial direction, in assembling the first casing, the second casing andthe blade ring. In this configuration, overhang of the blade ring can bereduced.

More specifically, by holding the blade ring with respect to the casingvia the third coupling flange located at substantially a central portionof the blade ring in the axial direction, the overhang of the blade ringcan be reduced as compared with the pot-like structure described inJapanese Unexamined Patent Application, Publication No. S59-213907. Inthis configuration, holding precision of the center of the blade ringwith respect to the rotor shaft is enhanced. Further, since the bladering is supported at substantially the central portion in the axialdirection, thermal extension of the blade ring in the axial directioncan equally be distributed.

In the above aspect, it is preferable that an inner peripheral side of aconnection member disposed between the blade ring and the casingprojects from the high-pressure side toward the low-pressure side of theworking fluid. In other words, it is preferable that the joining memberis a conical member which is disposed between the blade ring and thethird coupling flange, and which inclines from the high-pressure side tothe low-pressure side of the working fluid flowing between the rotorblade and the stator blade radially outward around the rotor shaft.

In this configuration, since the connection member functions as an endplate of the pressure vessel, strength of the connection member isenhanced.

According to the above aspect, the casing is divided into two in theaxial direction. Thus, leakage of the working fluid to outside thecasing and inflow of another fluid into the casing are reduced ascompared with a case where the casing is divided into two on thehorizontal surface. That is, there is no joining surface of the flangein the penetrating portion of the rotor shaft, leakage of the workingfluid to outside the casing and inflow of another fluid into the casingare reduced.

In the above aspect, an outer peripheral surface of the third couplingflange sandwiched between the first and second coupling flanges of thefirst and second casings divided in the axial direction may be enclosedbetween the first and second coupling flanges. In other words, the firstcoupling flange and the second coupling flange may be directly joined toeach other radially outside around the rotor shaft, and the firstcoupling flange and the second coupling flange may be joined radiallyinside with the third coupling flange sandwiched therebetween.

In this configuration, only one flange coupling surface is provided onthe outer peripheral surface of the casing and the range of the joiningsurface can be reduced. Therefore, leakage of the working fluid tooutside the casing and inflow of another fluid into the casing arefurther reduced.

In the above aspect, it is preferable that a pressure vesselaccommodating the casing therein is provided outside the casing, and afluid with a pressure higher than the working fluid flowing between therotor blades and the stator blades is filled in a space between thecasing and the pressure vessel.

According to the above aspect, the working fluid is prevented fromflowing into the space between the casing and the pressure vessel bycharging a fluid having pressure higher than that of the working fluidinto the space. Therefore, the working fluid is prevented from flowingoutside the casing.

According to the rotary machine of the present invention, the casing isdivided into two in the axial direction, there are effects that thecasing and the pressure vessel (outer casing) enclosing the casingtherein can be reduced in size, leakage of the working fluid to outsidethe casing and inflow of another fluid into the casing are reduced, andreliability and performance of the rotary machine are enhanced.

Further, holding precision of the center of the blade ring with respectto the rotor shaft is enhanced, and reliability of the rotary machine isenhanced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram for describing an entire configuration ofa gas turbine according to a first example of the present invention.

FIG. 2A is a schematic plan view of an axial two piece-configuration ofa casing structure.

FIG. 2B is an axial schematic side view of the axial twopiece-configuration of the casing structure.

FIG. 3A is a schematic plan view of a horizontal two piece-configurationof the casing structure.

FIG. 3B is an axial schematic side view of the horizontal twopiece-configuration of the casing structure.

FIG. 4 is a schematic diagram for describing an entire configuration ofa gas turbine according to a second example of the present invention.

FIG. 5 is a schematic diagram for describing a configuration in which acasing of a gas turbine is accommodated in a pressure vessel.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A casing structure of a gas turbine and the gas turbine having such acasing structure according to an embodiment of the present inventionwill be described with reference to FIGS. 1 to 5.

FIG. 1 is a schematic diagram for describing an entire configuration ofthe gas turbine according to a first example of the present invention.

As shown in FIG. 1, a gas turbine (rotary machine) 100 includes a casing101 constituting an outer shape of the gas turbine 100, a blade ring 3which holds turbine stator blades 10 on an inner periphery thereof, arotor shaft 4 in which turbine rotor blades 11 are embedded, an inletscroll portion 5 which supplies a working fluid to a first stage of theturbine stator blades 10, and a discharge scroll portion 6 into whichthe working fluid discharged from a last stage of the turbine rotorblades 11 flows.

In the gas turbine 100, the working fluid is accelerated by the turbinestator blades 10, the turbine rotor blades 11 are blown with theaccelerated working fluid, and thermal energy of the working fluid isconverted into mechanical rotation energy. The rotor shaft 4 is rotatedand power is thus taken out. There are generally provided the pluralityof turbine stator blades 10 and turbine rotor blades 11.

As shown in FIG. 1, the casing 101 constitutes the outer shape of thegas turbine 100. The blade ring 3, the rotor shaft 4, the inlet scrollportion 5 and the discharge scroll portion 6 are accommodated in thecasing 101. The casing 101 is divided into two, namely a high-pressurecasing 1 (first casing) and a low-pressure casing 2 (second casing), atsubstantially a central portion in a direction along the rotor shaft 4.

The casings 1 and 2 are substantially cylindrical members whose one endsthereof are closed. In other words, the casings 1 and 2 are bottomedcylindrical members, or so-called pot-like members. Outer peripheralportions of the open ends of the casings 1 and 2 have flanges 1A and 2A,respectively. The open ends of the casings 1 and 2 butt against eachother, the casings 1 and 2 are fastened to each other with a flange 3Aof the later-described blade ring 3 interposed between the flanges 1Aand 2A.

A through hole 7 into which the rotor shaft 4 is inserted is formed inclosed ends of the casings 1 and 2. An opening 8 into which a tube isinserted is provided in cylindrical surfaces of the casings 1 and 2. Theworking fluid flows into or out of the tube.

As shown in FIG. 1, the blade ring 3 surrounds the rotor shaft 4together with the casings 1 and 2, constitutes the gas turbine 100 andsupports the turbine stator blades 10.

The blade ring 3 includes a substantially cylindrical member extendingin the axial direction around a rotational axis L, the flange 3Adisposed on the outermost peripheral portion, and substantially conicalconnection member 3B which holes the substantially cylindrical bladering member by the flange 3A, and the flange 3A is sandwiched betweenthe flanges 1A and 2A. The turbine stator blades 10 are held on theinner periphery of the blade ring 3. The flange 3A is located atsubstantially the center of the axial length of the blade ring 3.

The turbine rotor blades 11 are embedded in the rotor shaft 4, and asshown in FIG. 1, the turbine rotor blade 11 is blown with the workingfluid accelerated by the turbine stator blades 10, so that the rotorshaft 4 is rotated and driven around the rotational axis L. Generally,the plurality of turbine stator blades 10 and the plurality of turbinerotor blades 11 are alternately provided, but a known configurations maybe employed thereto with no special limitation.

As shown in FIG. 1, the working fluid flows through the inlet scrollportion 5 and the discharge scroll portion 6. The inlet scroll portion 5supplies the working fluid to the first stage of the turbine statorblades 10, and the working fluid discharged from the last stage of theturbine rotor blades 11 flows into the discharge scroll portion 6.

Operation of the gas turbine 100 having the above-describedconfiguration will be described next.

As shown in FIG. 1, in a high-temperature gas furnace, the working fluidheated to a high temperature flows into the inlet scroll portion 5 ofthe gas turbine 100. The working fluid which has flowed into the inletscroll portion 5 flows into an annular channel 31, and flows into acylindrical channel 32 at substantially a constant flow rate in thecircumferential direction. The working fluid which has flowed into thecylindrical channel 32 is introduced toward the first stage of theturbine stator blades 10.

As shown in FIG. 1, the turbine rotor blades 11 are rotated and drivenby the flowing working fluid, and a rotational driving force extractedby the rotor blades 11 is transmitted to the rotor shaft 4. The workingfluid of which rotational driving force is extracted by the turbinerotor blades 11 and of which temperature is lowered is discharged fromthe last stage of the turbine rotor blades 11.

The working fluid which was discharged from the last stage of theturbine rotor blades 11 flows into the cylindrical channel 32 of thedischarge scroll portion 6 as shown in FIG. 1, and flows toward theannular channel 31. The working fluid which has flowed into the annularchannel 31 is discharged from the discharge scroll portion 6, i.e., fromthe gas turbine 100, and is again introduced into the high-temperaturegas furnace through each system.

According to the above configuration, in a case where the casing 101 isdivided into two in the axial direction, the casing 101 can be reducedin size as compared with a casing which is divided into two on ahorizontal surface. More specifically, the flanges 1A and 1B used forfastening the divided casings 1 and 2 to each other project outward fromthe entire periphery of the casing 101. However, since the area of thecross section which is vertical in the axial direction is smaller thanthat of a horizontal cross section, a range of projections of theflanges can be made smaller in the casing which is axially divided intotwo as compared with a configuration in which the casing is divided intotwo on the horizontal surface.

FIGS. 2A, 2B, 3A, and 3B schematically show the above-describedconfiguration.

FIGS. 2A and 2B show a casing structure of a gas turbine in the axialtwo piece-configuration, and are respectively a plan view and a sideview as viewed from the axial direction. Hatched portions 1A and 1Bindicate connection flanges provided on the casings 1 and 2 which aredivided in the axial direction, and the connection flanges project fromthe casings 1 and 2. The entire length of the casing 101 is defined asL1, and the diameter of the casing 101 is defined as D1. In a generalgas turbine, L1 is greater than D1. Here, when a cylindrical pressurevessel is provided outside the casings 1 and 2, an outer shape of thepressure vessel is shown with a chain double-dashed line 200, and itslength is defined as L2 and its diameter is defined as D2.

FIGS. 3A and 3B show a casing structure of a gas turbine in which thecasing is divided into two on a horizontal surface, and are respectivelya plan view and a side view as viewed from the axial direction. Hatchedportions 111A and 111B indicate connection flanges provided respectivelyon a casing 111 located on the upper side (upper casing) and a casing112 located on the lower side (lower casing) in the casing divided onthe horizontal surface, and the connection flanges project radiallyoutward and axially outward from the casing 111 and the casing 112around the rotational axis L. The entire length of the casing 101 isdefined as L1, and a diameter of the casing 101 is defined as D1. In thegas turbine itself in the same shape, L1 and D1 of the case where thecasing is axially divided into two (configuration of the presentembodiment) and those of the case where the casing is divided into twoon the horizontal surface are the same. When the cylindrical pressurevessel is provided outside the casing 111 and the casing 112, the outershape of the pressure vessel is shown with chain double-dashed line 210,and its length is defined as L3 and its diameter is defined as D3.

As apparent from the drawings, the region of the hatched portion of theaxial two piece-configuration (configuration of the present embodiment)shown in FIGS. 2A and 2B is smaller than that of the horizontal twopiece-configuration (conventional configuration) shown in FIGS. 3A and3B. That is, the range of the projections of the flanges is small.

Also in the case where the pressure vessel is provided outside thecasing 101, while the diameter D2 of the axial two piece-configurationand the diameter D3 of the horizontal two piece-configuration are equalto each other, the length L2 of the axial two piece-configuration can bereduced relative to the length L3 of the horizontal twopiece-configuration by the width of projections of the flanges.

In this configuration, the casing 101 can be reduced in size, thematerial cost and producing cost can be reduced, and the mass of theentire gas turbine 100 can be reduced. Therefore, it becomes easy tomove the gas turbine 100 for inspection or other purposes, andmaintainability is enhanced. When the pressure vessel 200 is providedoutside the gas turbine 100, the gas turbine can be also reduced insize, the material cost and producing cost can be reduced, and a gasturbine room can be reduced in size. In a general gas turbine, since thelength L1 is longer than the diameter D1 as described above, the axialtwo piece-configuration results in reduction in size of the casing 101.

According to the above configuration, the casings 1 and 2 and the bladering 3 are assembled by sandwiching the flange 3A of the blade ringbetween the coupling flanges 1A and 2A of the casings 1 and 2. Then,overhang of the blade ring 3 can be reduced. More specifically, when theblade ring 3 is held at the substantially central portion in the axialdirection with respect to the casing, the overhang of the blade ring 3can be reduced as compared with the pot-like structure. In thisconfiguration, precision of center hold of the blade ring 3 is enhancedwith respect to the rotor shaft 4. Further, since the blade ring 3 issupported at substantially the central portion in the axial direction,axial thermal extension of the blade ring 3 can be equally distributed,and reliability of the gas turbine 100 is enhanced.

According to the above configuration, the connection member 3B of theblade ring 3 functions as an end plate in the pressure vessel. A region12 surrounded by the casing 1 and the blade ring 3 is located on theinlet of the working fluid, and a region 13 surrounded by the casing 2and the blade ring 3 is located on the outlet of the working fluid.Therefore, a pressure in the region 12 is higher than a pressure in theregion 13. Thus, when the inner periphery of the connection member 3 inthe radial direction projects from the high-pressure region 12 to thelow-pressure region 13, resistance to pressure of the connection member3B is enhanced.

Although the connection member 3B is a substantially conical member inthe present embodiment, the connection member 3B may have a curvedsurface as long as it functions as an end plate. In a case wherestrength required to the connection member 3B is relatively small due toa pressure difference between the regions 12 and 13, the connectionmember 3B may be of a flat-plate, and the shape thereof is notespecially limited.

According to the above configuration, when the casing 101 is dividedinto two in the axial direction, leakage of the working fluid to outsideand inflow caused by entrainment of another fluid into the casing fromoutside can be reduced as compared with the horizontal twopiece-configuration. More specifically, since there is no flange joiningsurface provided in the penetrating portion of the rotor shaft, leakageof the working fluid to outside the casing and inflow of another fluidinto the casing are further reduced.

According to the above configuration, by dividing the casing 101 intotwo in the axial direction, an internal pressure load applied by thepressure of the working fluid to the coupling flanges of the dividedsurface can be equalized and reduced as compared with the casing isdivided into two on the horizontal surface.

When the casing is divided into two on the horizontal surface, since ahigh pressure portion and a low pressure portion exist in the casing asdescribed above, the internal pressure load applied to the couplingflanges is varied depending upon locations. Therefore, it is necessaryto take such variation into consideration upon designing strength of abolt for fastening flanges or strength of the flanges itself. When thecasing 101 is divided into two in the axial direction, since a loadapplied to the flanges 1A and 2A becomes constant in the circumferentialdirection, it becomes easy to design the strengths of the flanges andthe fastening bolt. As schematically shown in FIGS. 2A, 2B, 3A, and 3B,the internal pressure load applied to the flanges can also be reduced.

In the axial two piece-configuration, a pressure receiving area A1 ofthe flange joining portion is substantially calculated by the followingequation (1),

A1=π×D1/4  (1)

wherein, π represents the circle ratio.

In the horizontal two piece-configuration, a pressure receiving area A2of the flange joining portion is substantially calculated by thefollowing equation (2).

A2=L1×D1  (2)

In this case, because of π≈3.14 and L1>D1, it can be found that A1 issmaller than A2 from the following equation (3).

A1=π×D1²/4<D1² <L1×D1=A2  (3)

When the pressure applied to a division surface in the axial twopiece-configuration and the horizontal two piece-configuration isobtained by averaging the pressure of the high pressure portion and thepressure of the low pressure portion, which are equal to each other, theinternal pressure load applied to the flanges is determined by thepressure receiving area. Thus, the inner pressure load is lower in theaxial two piece-configuration.

Second Embodiment

FIG. 4 is a schematic diagram for describing an entire configuration ofa gas turbine according to a second example of the present invention. Abasic configuration of the gas turbine of the present example is thesame as that of the first example, but a holding structure of the thirdcoupling flange is different from that of the first example. In thepresent example, only the holding structure of the third coupling flangewill be described with reference to FIG. 4, and description of otherconstituent elements will not be repeated. The constituent elements sameas those of the first example are designated with the same symbols, anddescription thereof will not be repeated.

In the second example, as shown in FIG. 4, an outer peripheral surfaceof the flange 3A sandwiched between the flanges 1A and 1B of the casings1 and 2 obtained by axially dividing into two the casing 101 of a gasturbine 300 is incorporated between the flanges 1A and 1B.

In the first example, the flange 3A is sandwiched between the flanges 1Aand 2A of the casings 1 and 2. Therefore, there are provided two flangejoining surfaces on the outer periphery of the casing 101. On the otherhand, according to the configuration of the second example, since anouter peripheral portion 3C of the flange 3A is incorporated between theflanges 1A and 2A, the flanges 1A and 2A are directly joined to eachother on the outer periphery of the casing 101. In this configuration,the number of joining locations is one, and the peripheral length of thejoining surface can be reduced to substantially half. Accordingly,leakage of the working fluid to outside the casing and inflow of anotherfluid into the casing are reduced.

According to the above-described configuration, the peripheral length ofthe cross section of the flange joining portion is shorter in the axialtwo piece-configuration with respect to that of the horizontal twopiece-configuration. When the casing 101 is divided into two in theaxial direction, the range of the joining surface can be reduced ascompared with the case where the casing is divided into two on thehorizontal surface. Accordingly, leakage of the working fluid to outsidethe casing and inflow of another fluid into the casing are reduced.

FIGS. 2A, 2B, 3A, and 3B schematically show the above configuration.

As described also in the first example, FIGS. 2A and 2B show the casingstructure of the gas turbine of the axial two piece-configuration, andare respectively a plan view and a side view as viewed from the axialdirection. The hatched portions 1A and 1B indicate the connectionflanges provided on the casings 1 and 2 which are divided into two inthe axial direction. In a general gas turbine, the length L1 of thecasing 101 is longer than the diameter D1. The peripheral length L10 ofthe cross section of the flange joining portion is substantiallycalculated by the following equation (4),

L10=π×D1  (4)

wherein, π represents the circle ratio.

FIGS. 3A and 3B show the casing structure of the gas turbine dividedinto two on the horizontal surface, and are respectively a plan view anda side view as viewed from the axial direction. The hatched portions111A and 111B indicate the connection flanges provided respectively onthe casing 111 and the casing 112 divided on the horizontal surface.Similarly, when the entire length of the casing 101 is defined as L1 andthe diameter of the casing is defined as D1, a peripheral length L11 ofthe cross section of the flange joining portion is substantiallycalculated by the following equation (5).

L11=2×(L1+D1)  (5)

Because of π≈3.14 and L1>D1, it can be found that L10 is smaller thanL11 from the following equation (6).

L10=π×D1<2×(D1+D1)<2×(L1+D1)=L11  (6)

Accordingly, the peripheral length of the cross section of the flangejoining portion is shorter in the axial two piece-configuration withrespect to that in the horizontal two piece-configuration. When thecasing 101 is divided into two in the axial direction, the range of thejoining surface can be reduced as compared with the case where thecasing is divided into two on the horizontal surface. Accordingly,leakage of the working fluid to outside the casing and inflow of anotherfluid into the casing can further be reduced, and thus, reliability ofthe gas turbine 300 can be enhanced.

The scope of the present invention is not limited to the aboveembodiments, and the present invention can variously be modified withina range not departing from the subject matter of the invention.

For example, although the present invention is applied to the axial-flowturbine in the above embodiments, the present invention is not limitedto the axial-flow turbine, but the present invention can also be appliedto other kinds of turbines such as a centrifugal type turbine and adiagonal-flow turbine.

The present invention can also be applied to a general rotary machine ofa gas turbine of another type in which air is used as a working fluidand combustion energy of fossil fuel is used as a heat source, a steamturbine, a compressor, or a pump, with no special limitations.

1. A rotary machine, wherein a first casing and a second casing formedby dividing a substantially cylindrical casing, enclosing in theinterior thereof a rotor shaft in which rotor blades are embedded, intotwo at substantially a central portion relative to an axial direction ofthe rotor shaft are provided; a first coupling flange and a secondcoupling flange are provided at openings in the first casing and thesecond casing, respectively; a third coupling flange is provided, whichis enclosed by the casing, which is positioned at substantially acentral portion of the length in the axial direction in a substantiallycylindrical blade ring holding stator blades and enclosing the rotorshaft, and which holds the blade ring; the first casing, the secondcasing, and the blade ring being assembled by sandwiching the thirdcoupling flange between the first coupling flange and the secondcoupling flange.
 2. A rotary machine according to claim 1, wherein theblade ring is held relative to the third coupling flange by asubstantially conical joining member, and an inner peripheral surface atthe blade ring side of the joining member projects from a high-pressureside to a low-pressure side in a working fluid flowing between the rotorblades and the stator blades.
 3. A rotary machine according to claim 1,wherein an outer peripheral portion of the third coupling flange iscontained between the first coupling flange and the second couplingflange.
 4. A rotary machine according to claim 1, wherein a pressurevessel accommodating the casing therein is provided outside the casing,and a fluid with a pressure higher than the working fluid flowingbetween the rotor blades and the stator blades is filled in a spacebetween the casing and the pressure vessel.